1. Field of Invention
Differing from crude petroleum which exists as oil in the pores of porous sands, organic matter in oil shale is believed to exist in solid form called kerogen. Crude shale oil is typically produced from oil shale by decomposition of the kerogen by heating. Crude shale oil differs from crude petroleum because, in addition to saturated and unsaturated hydrocarbons, it contains hydrocarbons, both saturated and unsaturated, in chemical and/or physical combination with a substantial amount of nitrogen, sulfur, and oxygen when compared to the elemental levels of petroleum crude. It is because of this property that crude shale oil requires additional treating when shale oil is refined by conventional petroleum refining techniques and procedures. For example, conventional refinery catalytic reforming and cracking processes can not be used to treat shale oil because of excessive carbon or coke formation and/or poisoning of active catalyst sites, which is attributable to substantial amounts of nitrogen and sulfur present in shale oil. Accordingly, an improved economical process for upgrading crude shale oil is needed to prepare a stock suitable for cracking or further refining.
2. Description of the Prior Art
"The first recorded reference to processing oil shale is in a patent issued in England in 1694 to distill `oyle from a kind of stone.`" Encyclopedia of Chemical Technology, Second Edition, Volume 18, (John Wiley & Sons, Inc., 1969), p. 9. In the past, upgrading of shale oil has been performed commercially by one-stage hydrogenation or two-stage hydrogenation, such as that disclosed in U.S. Pat. No. 3,481,867 to Delbert, or by hydrogenation followed by an acid extraction process, as disclosed in U.S. Pat. No. 2,692,226 to Smith. Unfortunately, one- and/or two-stage hydrogenation processes require excessive use of hydrogen, and the two-stage hydrogenation-acid extraction process results in an acid sludge which is an industrial and environmental problem.